The overall objective of the proposed research is to develop and apply the use of external reflection infrared spectroscopy as an analytical method to observe, in-situ, the infrared spectra of insoluble model biomembrane monolayers at the air-water interface. While biomembrane monolayers at the air-water interface have been extensively used as models for membrane bilayers and interfacial phenomena, there is virtually no information available concerning the detailed physical structure of these systems. We propose to apply infrared spectroscopy to the in-situ study of these thin films in order to more precisely described their structure, dynamics, and interfacial properties. The research described in this proposal would be the first to utilize vibrational spectroscopy to directly measure the molecular-level physical structure of these model membrane films at the air-water interface. A manual langmuir-Blodgett film balance has been fabricated and interfaced to an FT-IR spectrometer in our laboratory. We propose to study increasingly more complex biophysical surface films with this experimental design. Specifically, we intend to perform the following experiments: (1) Study the thermodynamic phase transitions of phospholipid monolayer films, (2) characterize the interfacial chemistry of the membrane surface as surface- active agents interact with the membrane interface, (3) study protein monolayers and lipid-protein complexes at the air-water interface to try to measure-induced conformational changes, and (4) study monolayers of pulmonary lung surfactant as a natural, physiologically relevant monolayer. Professor K.M.W. Keough of Memorial University, St. John's Newfoundland, has agreed to collaborate on the lung surfactant studies. The results of these studies should shed new light on the physical structure of a variety of widely used biomembrane models.